Downhole tools, used in wellbore operations, may require actuation downhole. Because of the distance from surface and downhole rigors, reliable actuation of downhole tools is often difficult.
“Controllable fluids” are materials that respond to an applied electric or magnetic field with a change in their rheological behavior. Typically, this change is manifested when the fluids are sheared by the development of a yield stress that is more or less proportional to the magnitude of the applied field. These materials are commonly referred to as electrorheological or rheomagnetic (also known as magnetorheological) fluids. Interest in controllable fluids derives from their ability to provide simple, quiet, rapid-response interfaces between electronic controls and mechanical systems. Controllable fluids have the potential to radically change the way electromechanical devices are designed and operated.
Rheomagnetic fluids are suspensions of magnetically responsive, polarizable particles having a size on the order of a few microns in a carrier fluid. Typical carrier fluids for magnetically responsive particles include hydrocarbon oil, silicon oil and water. The particles in the carrier fluid may represent 25-45% of the total mixture volume. Such fluids respond to an applied magnetic field with a change in rheological behavior. Polarization induced in the suspended particles by application of an external field causes the particles to form columnar structures parallel to the applied field. These chain-like structures restrict the motion of the fluid, thereby increasing the viscous characteristics of the suspension.